Binomial and Hypergeometric Probabilities

A city has 4050 children under the age of 10, including 514 who have not been vaccinated for measles. 65 of the city's children are enrolled in the ABC Day Care Center. Suppose the municipal health department sends a doctor and a nurse to ABC to immunize any child who has not already been vaccinated.
Find a formula for the probability that exactly k of the children at ABC have not been vaccinated.